AGRIC,  DEFT, 


»• 


1.    Studies  on  Hybrid  Ducks 


H.  D.  GOODALE 


Reprinted  from  THE  JOURNAL  OF  EXPERIMENTAL 
ZOOLOGY,  Vol.  10,  No.  3,  April,  1911 


iflafo  Lib. 


Reprinted  from  THE  JOURNAL  OF  EXPERIMENTAL  ZOOLOGY,  VOL.  10,  No.  3 
April,  1911 


0/1    L 

STUDIES  ON  HYBRID  DUCKS 

H.   D.  GOODALE 

NINE    FIGURES 
TWO   PLATES 

As  no  studies  from  a  Mendelian  standpoint  seem  to  have  been 
made  on  ducks,  the  following  experiments  were  undertaken. 
The  results  thus  far  obtained  are  sufficiently  interesting  and 
suggestive  to  make  a  first  report  on  the  work  'in  progress  desir- 
able. The  record  shows  that  too  few  individuals  in  the  Fi  gen- 
eration have  been  reared  to  make  much  theoretical  discussion 
profitable. 

My  thanks  are  due  Mr.  B.  B.  Horton  for  permitting  me  to 
carry  on  this  work  at  "Oakwood." 

"  j> 

DESCRIPTION   OF  BREEDS 

The/ two  breeds  used,  which  were  crossed  reciprocally,  were 
the  Pekins  and  Rouens.  It  is  well  known  that  both  varieties 
breed  true.  Some  200  of  the  former  and  40  of  the  latter  have 
been  reared,  and  without  exception  have  been  true  to  type. 

The  Pekins  (fig.  1  )  are  white  with  yellow  bills.  The  shanks 
and  feet  are  orange.  The  ducklings  are  yellow  throughout. 

The  Rouens  are  practically  domesticated  Mallards.  The  male 
(fig.  2)  is  brilliantly  colored.  His  head  and  the  upper  half  of 
the  neck  is  deep  lustrous  green,  bounded  on  its  lower  edge  with 
a  narrow  white  ring,  often  incomplete  dorsally.  The  ventral 
side  of  the  lower  half  of  the  neck,  together  with  the  breast  (i.  e., 
anterior  to  keel)  is  a  deep  claret  (maroon).  The  remainder  of 
the  ventral  surface  is  iron  gray,  becoming  black  posterior  to  the 
anus.  The  entire  dorsal  surface,  posterior  to  the  neck  ring,  is 
dark,  being  dull  brownish  anteriorly,  becoming  black  in  the 

241 


320869 


242  H.    D.    GOODALE 

middle  of  the  back,  and  greenish  black  on  the  rump.  All  the 
gray  feathers,  scapulars,  and  the  anterior  dorsal  feathers  are 
vermiculated.  The  main  tail  feathers  are  dull  black.  A  specu- 
lum of  iridescent  purple  is  formed  by  the  major  part  of  the  exposed 
surface  of  the  secondaries.  The  under  side  of  the  wing,  not 
including  the  remiges,  is  creamy  white.  The  bill  is  light  greenish 
yellow.  The  shanks  and  feet  are  orange.  The  female,  (fig.  3), 
by  contrast,  is  rather  plain  colored.  On  the  whole  she  may  be 
described  as  streaked  dark  brown  and  buff.  The  upper  surface 
is  considerably  darker  than  the  ventral.  The  throat  and  sides 
of  the  head  are  buff  with  two  dark  stripes  passing  across  the 
latter  (fig.4A).  There  is  no  neck  ring.  The  speculum  and  under 
surface  of  the  wing  are  the  same  as  in  the  male.  The  bill  is  dull 
brownish  black,  with  greenish  yellow  blotches.  The  shanks  and 
feet  are  orange.  The  newly  hatched  Rouen  duckling  of  both 
sexes  is  dull  black  with  two  dull  yellow  stripes  on  each  side  of 
the  head  and  with  some  dull  yellow  spots  on  the  body. 

THE  F!  GENERATION 

Owing  to  the  method  of  making  the  matings  the  individual 
mothers  of  the  Fi  generation  are  not  known.  A  Rouen  male  was 
placed  in  a  pen  of  Pekin  females  and  vice  versa.  There  were  23 
young  hatched  from  both  matings,  13  were  hatched  here  in  1909; 
6  had  Rouen  mothers,  7  Pekin.  The  other  10,  all  Pekin  males 
by  Rouen  females,  were  hatched  and  reared  for  me  by  my 
brother  in  1910.  Their  parents  were  from  my  own  stock.  Of 
these  I  personally  saw  only  5  females  as  adults.  Besides  these 
there  were  nearly  a  dozen  others  from  the  same  matings,  but  in 
which  the  ducklings  from  the  reciprocal  crosses  were  mixed 
together  owing  to  an  oversight  at  hatching  time. 

FI  ducklings.  Part  of  the  FI  ducklings  belonged  to  the  Rouen 
type.  The  remainder  had  a  new  type  of  down.  These  were  dull 
yellow,  very  different  from  the  Pekin  color,  and  with  an  under 
color  of  dull  black  which  usually  came  to  the  surface  on  the  wings 
and  tail.  This  type  probably  represents  an  incomplete  dominance 
of  the  Rouen  down  over  the  Pekin.  The  only  exceptions  to  these 


STUDIES    ON    HYBRID    DUCKS  243 

forms  were  two  black  ducklings  which  appeared  among  the  dozen 
mentioned  above. 

FI  adults.  From  the  mating  Rouen  female  and  Pekin  male, 
seven  females  and  five  males  grew  to  maturity.  From  the  recip- 
rocal mating  there  were  two  females  and  three  males.  These 
were  all  pigmented  and  on  the  whole  closely  resembled  the  Rouens. 
When,  however,  the  various  characters  were  considered  separately 
it  was  found  that  the  hybrids  differed  in  several  points  from  the 
Rouens,  as  will  appear  from  the  following  description.  Besides 
these  there  were  two  greenish  black  females  with  white  throats 
and  breasts  (fig.  7).  They  appeared  among  the  lot  of  hybrids 
in  which  the  reciprocal  crosses  were  mixed. 

The  males  (fig.  5),  generally  speaking,  are  all  alike,  such  varia- 
tion as  was  noted  being  one  of  degree  rather  than  kind.  The 
head  is  identical  with  that  of  the  male  Rouen.  The  rest  of  the 
body  is  usually  somewhat  lighter  in  tone,  so  that  the  hybrids 
appear  brighter  than  the  Rouen  male.  There  is  a  neck  ring, 
several  times  as  broad  as  that  of  the  Rouen  in  all  the  males. 
The  claret  feathers  of  the  breast  are  partly  white,  especially  in 
the  midline.  On  the  other  hand,  the  feathers  of  the  dorsal  side 
of  the  lower  neck  contain  much  claret.  The  dorsal  surface  of  the 
wing  usually  is  quite  different  from  the  Rouen.  The  anterior 
third  is  nearly  white,  due  to  the  presence  of  a  broad  white  margin 
to  each  feather.  The  next  three  rows  or  thereabouts  have  less 
white,  but  present  a  broad  submarginal  band  of  rufous,  which 
becomes  less  conspicuous  in  the  next  two  rows.  The  next  row, 
which  lies  directly  over  the  remiges,  is  not  especially  modified. 
A  variable  number  of  the  primaries  are  always  white.  The  main 
tail  feathers  may  have  white  or  vermiculated  margins.  Vermicu- 
lations  may  also  appear  in  sections  where  they  do  not  occur 
in  the  pure  Rouen.  There  is  one  male,  however,  in  which  the 
breast  and  the  dorsal  surface  of  the  wing  is  the  same  as  that  of 
the  thorough-bred  Rouen.  This  may  be  merely  a  variation  in 
dominance,  or  it  may  have  greater  significance. 

The  females  (fig.  6),  with  the  two  exceptions  already  noted, 
are  also  brighter  colored  than  the  female  Rouens,  but  not  more 
so  than  what  I  am  informed  is  the  fancier's  ideal.  The  brighter 


244 


H.    D.    GOOD ALE 


color  is  due  to  the  presence  on  the  feathers  of  more  buff  and  less 
black  than  occurs  in  the  Rouens  as  I  have  bred  them.  The 
most  striking  point  about  the  females  is  that  in  respect  to  a  given 
character  they  can  be  divided  into  two  classes,  viz.,  those  with 
and  those  without  the  character.  Some  characters,  e.  g.,  neck 
ring,  are  present  or  absent  in  the  female  irrespective  of  the  direc- 
tion in  which  the  cross  was  made.  But  the  data  at  hand  are 
insufficient  to  make  a  statement  of  any  value  regarding  other 
characters  studied.  The  important  point  at  present  is  the 
existance  of  two  classes  of  females,  in  respect  to  certain  characters, 
while  the  males  all  fall  into  one  class.  Thus,  while  all  the  males 
have  broad  neck  rings,  only  part  of  the  Fi  females  have  any 
ring  at  all.  Two  of  the  females  lack  the  head  stripes  (fig.  4B). 
In  addition,  there  are  the  two  black  females.  There  appear 

TABLE  1 
FI  pigmented  males 


NOT  INCLUDING   BLACK 

INCLUDING  BLACK 

Like  Rouen 
male 

Modified 

Like  Rouen 
male 

Modified 

Head  

7 
7 
6i 
7 
3 
6 
4 
0 
1 
4 
0 
3 
4 
4 
6 

0 
0 
0 

0 

42 

I6 

32 
62 
52 

22 

62 
32 
2* 
24 
0 

8 
8 
7 
7 
3 
6 
5 
1 
2 
4 
1 
3 
4 
4 
6 

0 
0 
0 
I6 

42    n 

2« 
32 
62 
52 
32 

62 
32     11 

3s 
34 
1» 

Bill  

Chin  spot8       

Neck  ring  

Breast  

Claret     

Rump     

Tail  

Under  tail  coverts  

Belly      

Primaries  

Upper  surface  of  wing  

Under  surface  of  wing  

Speculum  

Legs  and  feet 

1  The  difference  in  numbers  is  due  to  the  lack  of  records  on  one  male  recorded 
simply  as  "like  Rouen  drake."  2  With  much  white.  3  Pigmented.  4  Ob- 
scured. B  Pure  white.  6  Absent.  7  Black.  8  The  chin  spot  is  a  small 
white  spot  at  the  base  of  the  lower  mandible.  Among  the  pure  Rouens  I  have  seen 
it  only  in  the  males.  9  Black  and  orange. 


STUDIES   ON   HYBRID   DUCKS 


245 


TABLE  2 

F2  pigmented  females 


NOT   INCLUDING   BLACK 

INCLUDING   BLA.CK 

Like  Rouen 
female 

Modified 

Like  Rouen 
female 

Modified 

Head  

9 
9 
6 
5 
10 
7 
4 
8 
9 
9 
7 

21 
22 
53 
63 
I4 
44 
74 
34 
28 
26 
47 

9 
11 
6 

7 
10 
7 
4 
8 
9 
9 
7 

2i     2" 
22 
73 
63 
I4     2» 
54     I8 
94 
34    28 
45 

4« 
47    210 

Bill     

Chin  spot  

Neck  ring  

Breast  

Belly..  !  

Primaries  : 

Upper  surface  of  wing. 

Under  surface  of  wing  

Speculum  

Legs  and  feet  

1  Plain.        2  Nearly     yellow.        3  Present.        4  With     much     white.         E  Pig- 
mented.         8  Obscured.  7  With  some  black.  8  Black.  9  Pure  white 

10  Black  and  orange. 


also  tyo  be  several  other  characters  which  are  present  in  part  of 
the  females  and  absent  in  the  remainder,  but  which  are  either 
always  present  or  always  absent  in  the  male.  I  am  not  pre- 
pared at  present  to  speak  definitely  in  regard  to  these  characters 
mainly  because  this  peculiarity  in  their  inheritance  was  not 
noticed  until  the  F2  generation  was  studied  (tables  1  and  2).  On 
the  other  hand,  there  are  characters  which  are  in  only  part  of  the 
individuals,  of  each  sex.  Thus,  white  shading  on  the  breast 
and  the  white-red  dorsal  wing  surface,  as  described  for  all  but  one 
of  the  FI  males,  are  present  in  only  part  of  the  females.  But  I 
have  failed  to  find  any  character,  which  is  present  in  only  part 
of  the  males,  but  which  is  always  present  or  always  absent  in  all 
the  females.  The  significance  of  these  statements  will  be  con- 
sidered later  on  in  the  paper. 

The  two  greenish  black  individuals  (fig.  7)  with  white  throats 
and  breasts  resemble  strongly  the  variety  of  ducks  known  as 
Blue  Swedish.  One  died  at  an  early  age.  The  other  shows 


246  H.    D.    GOOD ALE 

traces  of  light  head  stripes.  She  has  some  white  primaries. 
The  under  side  of  her  wings  instead  of  being  white  are  light  brown 
with  darker  markings.  The  speculum  is  obscured,  apparently 
by  being  overlaid  with  black  pigment.  The  bill  is  nearly  black 
with  greenish  cast.  The  feet  contain  much  black  in  addition 
to  the  normal  orange.  The  occurrence  of  similar  black  ducks  has 
been  noted  in  two  other  flocks  composed  of  Pekins  and  Rouens. 

THE  F2  GENERATION 

The  F2  generation  is  a  motley  assemblage.  Unfortunately 
many  of  the  young  managed  to  lose  their  leg  bands  so  that  the 
exact  parentage  of  each  individual  in  not  known.  Consequently 
this  generation  will  have  to  be  considered  as  a  whole,  except  in 
the  case  of  pigmented  and  non-pigmented  down,  which  is  given 
in  connection  with  the  description  of  each  mating.  The  adults 
are  considered  under  a  separate  heading. 

A  record  of  the  down  plumage  of  each  duckling  was  made  at 
hatching  time.  The  only  correlation  between  down  and  adult 
plumage,  about  which  there  is  no  doubt,  is  that  existing  between 
yellow  ducklings  and  white  adults.  There  are  several  types  of 
down  among  the  pigmented  ducklings,  but  their  relation  to  the 
various  types  of  pigmented  adults  is  entirely  unknown,  so  that  the 
down  records  only  enable  us  to  separate  pigmented  from  non- 
pigmented  individuals. 

Fz  matings  and  down  color.  Two  pens  of  Fi  were  mated.  In 
one  a  drake  from  a  Pekin  female  by  Rouen  male  was  placed  with 
two  of  his  sisters.  Their  eggs  did  not  hatch  well  and  only  nine 
young  were  produced.  Six  had  pigmented  down  and  three 
yellow  down. 

In  the  other  pen  was  placed  a  drake,  derived  from  a  Rouen 
mother  and  Pekin  father,  with  one  of  his  sisters  and  the  FI  black 
duck  with  white  breast.  From  the  first  duck  there  were  five  pig- 
mented and  four  yellow  ducklings;  from  the  black  duck  there 
were  seven  pigmented  and  three  yellow  ducklings. 

Altogether  there  were  twenty-nine  F2  ducklings  from  these  two 
pens,  nineteen  were  pigmented  and  ten  yellow.  If  the  black 


STUDIES    ON    HYBRID    DUCKS  247 

duck's  progeny  is  left  out  of  consideration  there  are  twelve  pig- 
mented  and  seven  yellow  ducklings.  In  any  case  there  is  a  con- 
siderable excess  of  yellow  ducklings,  the  proportion  standing 
about  two  pigmented  to  one  yellow,  instead  of  the  expected  ratio 
of  three  to  one. 

Later  in  the  season,  a  Pekin  drake  was  substituted  for  the  hy- 
brid drake  in  the  second  pen.  There  were  seven  pigmented  and 
three  yellow  ducklings.  Only  one  was  reared,  a  male.  He  is 
not  included  in  the  table  given  below. 

A  mating  was  also  made  between  a  hybrid  male  and  a  Pekin 
female.  Only  three  ducklings  were  hatched,  two  pigmented  and 
one  yellow. 

Fi  adults.  The  chief  interest  in  the  F2  adults  attaches  to  the 
pigmented  types,  which  numbered  twenty-one  individuals,  thir- 
teen females  and  eight  males.  The  white  adults  are  identical 
with  the  Pekins.  The  distribution  among  the  pigmented  adults 
of  the  various  characters  studied  are  given  in  tables  1  and  2. 
But  there  are  also  some  points  which  require  a  more  extended 
treatment. 

Two  females  (fig.  7)  and  one  male  were  essentially  like  the  F! 
black  female,  though  the  male  and  one  of  the  females  had  a  small 
amount  of  white,  distributed  irregularly  on  the  head  and  neck. 
This  last  female  retained  her  leg  band.  Her  mother  proves  to 
be  the  black  FI  female  and  her  father  a  hybrid  male.  The  black 
male  has  no  white  neck  ring,  no  white  primaries  and  no  vermicu- 
lations.  His  is  the  only  case  in  which  these  characters  have 
been  found  absent  in  the  male.  His  head,  where  not  white,  is 
lustrous  green  as  in  normal  Rouen  males. 

The  other  eighteen  individuals,  show  mostly  Rouen  characters. 
In  one  male  the  claret  of  the  breast  is  wanting,  its  place  being 
taken  by  iron  gray  (fig.  8).  The  speculum  of  this  male  is 
obscured  and  the  under  side  of  the  wings  pigmented.  The  rest 
of  the  males  are  not  markedly  different  from  the  FI  males,  except 
that  the  width  of  the  neck  ring  varies  considerably. 

Two  of  the  females  are  much  marked  with  white  (fig.  9).  The 
neck  ring  extends  over  nearly  one-half  the  neck  and  reaches  up 
the  throat  to  the  lower  mandible.  There  is  a  large  white  patch 


PLATE  1 


EXPLANATION  OF  FIGURES 


1  Pekin  male.     X  about  1/10.     The  female  is  practically  the  same. 

2  Rouen,  male.     X  about  1/7. 

3  Rouen,  female.     X  about  1/8. 

4  A,  striped  head.     X  about  2/7;  B,  plain  head.     X  about  1/3. 


248 


STUDIES  ON  HYBRID?DUCKS 

H.  D.  GOODALE 


PLATE   1 


THE  JOURNAL,  OP  EXPERIMENTAL  ZOOLOGY,  VOL.  10,  NO.  3 

249 


PLATE  2 

EXPLANATION   OF   FIGURES 

5  FI  hybrid  male.     X  about  1/10. 

6  Ft  hybrid  female.     X  about  1/7. 

7  F2  white  breasted,  black  female.     X  about  1/8.     The  FI  black  female  is  prac- 
tically identical  with  this  one. 

8  F2  male  which  lacks  the  claret  breast.     X  about  1/7. 

9  F2  female,   X   about  1/9,  with  much  white  and  somewhat  resembling  an 
Indian  Runner  duck. 


250 


STUDIES  ON  HYBRID  DUCKS 

H.  D.  GOODAt/E 


PLATE  2 


251 


252  H.    D.    GOODALE 

on  the  belly  and  much  white  in  the  wings.  Judging  from  a  study 
of  the  other  females,  there  are  four  points  or  centers  for  the  origin 
of  these  white  areas,  viz.:  At  base  of  lower  mandible,  neck  ring, 
posterior  end  of  sternum  and  outer  primaries.  The  white  areas 
themselves  may  be  large  or  small.  They  may  all  be  present  or  all 
absent,  or  part  may  be  present  and  part  absent.  In  the  case  of 
the  two  females  under  consideration,  all  are  present  and  all  large, 
thus  producing  an  effect  which  calls  to  mind  the  pattern  of  Indian 
Runner  ducks.  Both  these  ducks  have  nearly  yellow  bills. 

One  female  has  a  noticeably  redder  breast  than  the  others. 
Its  meaning  is  uncertain. 

There  appears  to  be  a  curious  correlation  between  plain  head 
(fig.  4B)  (i.  e.,  head  without  stripes),  obscured  speculum  and 
pigmented  under  surface  of  the  wing.  There  are  four  cases  of 
plain  head  among  the  females,  not  including  the  black  individuals, 
two  in  FI  and  two  in  F2.  All  had  obscured  specula  and  all  had 
the  under  side  of  the  wing  pigmented.  All  the  blacks  have 
obscured  specula  and  the  under  surface  of  the  wing  pigmented, 
though  it  is  difficult  to  determine  whether  or  not  the  head  is 
really  striped. 

DISCUSSION 

The  data  which  I  have  been  able  to  present  are  too  meagre  to 
permit  of  much  discussion.  There  are,  nevertheless,  some 
features  which  are  strongly  suggestive. 

The  most  striking  thing  about  the  Fx  generation  is  the  appar- 
ently greater  heterogeneity  of  the  females  as  compared  with  the 
more  homogeneous  males.  A  description  of  one  FI  male  would 
fit  all  the  other  FI  males,  though,  of  course,  larger  numbers  might 
prove  this  statement  to  be  without  foundation.  The  evidence 
in  regard  to  certain  characters  is,  however,  fairly  strong.  All 
FI  males  have  a  white  neck  ring  and  white  primaries.  Further, 
leaving  out  of  consideration  for  the  present  the  summer  plumage, 
no  case  of  striped  head  has  been  seen  in  the  FI  males.  There  is 
similar  but  less  conclusive  evidence  in  regard  to  some  other  charac- 
ters. But  there  is  no  evidence  of  an  opposite  nature.  Since  in 


STUDIES    ON    HYBRID    DUCKS  253 

Fi  certain  characters  are  present  in  some  females  and  absent  in 
others,  and  since  in  the  males  the  same  characters  are  always 
present  (or  always  absent  according  to  the  character  in  question) 
it  appears  that  these  characters  are  sex  limited.  The  following 
generalized  formula  will  show  how  the  facts  may  be  interpreted, 
using  Bateson's  assumption  of  a  sex  homozygous  male  and  sex- 
heterozygous  female. 

S,  is  a  sex  limited  character;  s,  its  absence,  i.  e.  the  presence  of 
another  character.  The  PI  females  are  S  9  s  <? ;  the  males  S  cf 
s  cf .  Coupling  is  assumed  to  occur  between  9  and  s.  Or,  if 
prefered,  a  repulsion  between  9  and  S  may  be  assumed,  or  a 
coupling  between  d"  and  S.  The  Fi  then,  will  be  S  cf  S  cf ,  S  cf 

S  cf ;  S     cf   S  9,   S  cfS  9. 

The  Fi  males,  then,  will  be  visibly  alike,  though  of  two  gametic 
constitutions;  the  females  will  be  of  two  visible  classes. 

Before  going  further,  it  may -be  well  to  point  out  that  the  data 
at  hand  do  not  necessarily  support  Bateson's  theory,  for  the 
facts  can  also  be  represented  thus; 

Females  8989;  Males  s  9  S  cf,  giving  females  s  9  s  9,  s  9 
S  9  and  males  ScfS9,ScfS9. 

Random  matings  of  the  Fi  will  give  theoretical  results  in  F2 
agreeing  sufficiently  well  with  the  observed  results,  which  ever 
formula  is  used,  though  according  to  the  first  method  of  formula- 
tion, a  few  males  should  occur  without  the  character  in  question 
in  F2.  According  to  the  second  method  all  the  F2  males  should 
have  the  character  in  question.  The  F2  black  male  lacks  a  ring 
neck  and  white  primaries,  thus  rather  favoring  the  first  mode  of 
representation.  However,  it  will  probably  be  necessary  to  estab- 
lish suitable  strains,  before  the  bearing  of  the  experiments  on 
the  present  theories  of  sex  determination  becomes  perfectly  clear, 
but  the  experiments  indicate  unmistakably  the  existence  of  some 
sort  of  sex  limited  inheritance  with  respect  to  several  of  the  charac- 
ters studied. 

In  the  formula  given  above  I  have  assumed  that  both  sexes  of 
the  parent  stock  were  heterozygous  for  certain  characters.  I 
have  made  this  assumption  because  of  the  variety  of  forms  appear- 
ing in  FI  which  ordinarily  conforms  to  a  single  type.  The  unex- 


254  H.    D.    GOODALE 

pected  occurrence  of  such  characters  as  a  broad  neck  ring  in  the 
males  and  the  appearance  of  a  neck  ring,  plain  head  and  black 
individuals  among  the  females,  is  probably  due  to  the  presence 
of  cryptomeres  in  the  Pekins,  though  this  point  cannot  be  proved 
until  further  crosses  with  other  varieties  of  ducks  are  made. 
Ridgeway,  however,  mentions  in  passing  a  cross  between  Mus- 
covy- (black)  and  Aylesbury  (white) .  The  progeny  were  colored 
like  mallards.  His  figure  shows  a  very  broad  neck  ring. 

Thus,  in  many  respects  Fi  in  the  present  instance,  is  like  an  F2 
generation.  The  F2  generation  in  these  experiments  contains 
only  a  few  more  forms  than  FI.  Indeed,  with  larger  numbers, 
some  of  the  forms  which  have  appeared  only  in  F2  may  reasonably 
be  expected  to  appear  in  FI.  A  priori,  it  would  seem  more  prob- 
able that  the  heterozygous  males  occurred  among  the  Pekins. 
The  Pekins  may  easily  be  a  mixed  population  in  respect  to  numer- 
ous factors  rendered  invisible  by  the  white  plumage.  Some 
individuals  may  be  heterozygous  in  respect  to  a  given  character 
while  others  may  be  homozygous  either  for  the  presence  of  this 
character  or  for  its  absence.  The  introduction  of  color  has  made 
possible  the  isolation  of  pure  lines. 

As  the  individual  mothers  of  the  FI  generation  are  unknown,  it 
is  obvious  that  if  one  mother  were  homozygous  for  a  character 
and  another  heterozygous,  the  father  being  homozygous,  that 
the  observed  results  would  follow,  provided  that  it  is  also  assumed 
that  in  the  female  a  character  does  not  become  patent  except  in 
the  homozygous  condition,  though  patent  in  its  heterozygous 
condition  in  the  males.  Thus  the  case  would  be  paralleled  to  the 
inheritance  of  horns  in  sheep,  cited  by  Bateson. 

Not  all  characters  appear  to  be  correlated  with  sex.  White 
shading  of  the  breast  and  red-white  on  the  dorsal  wing  surface  is 
present  in  some  FI  individuals  of  both  sexes,  absent  in  others, 
thus  behaving  as  if  it  were  of  the  form  DR  in  both  parent  stocks, 
or  DR  in  one  and  RR  in  the  other.  The  evidence,  however,  is 
conclusive  that  at  least  one  of  the  parent  stocks  contains  individ- 
uals which  are  heterozygous  for  certain  characters. 


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